/**
 * Created by L.jp
 * Description:
 * User: 86189
 * Date: 2021-10-07
 * Time: 14:51
 */
class ListNode {
     int val;
     ListNode next;
     ListNode() {}
     ListNode(int val) { this.val = val; }
     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
}
public class MiddleNode {
    public ListNode middleNode(ListNode head) {
        if(head==null || head.next==null){
            return head;
        }
        ListNode fast=head;
        ListNode slow=head;
        while(fast!=null && fast.next!=null){
            fast=fast.next.next;
            slow=slow.next;
        }
        return slow;
    }
}
